Hydraulic periphery pumps conventionally include a housing having a drive shaft mounted for rotation about its axis. An impeller is coupled to the drive shaft for rotation within the housing, and has a disc-shaped body with axially opposed substantially flat side faces and a circumferential array of peripheral vanes. A pair of backup bearing plates are mounted within the housing and have flat inner faces slidably opposed to the flat side faces of the impeller. An arcuate fluid chamber is formed between the backup plates and the housing around the periphery of the impeller, and has angularly spaced fluid inlet and outlet ports. A periphery pump of this character, also called a tangential, turbine-vane, regenerative, turbulence or friction pump, produces pumping action by motion of the vaned periphery in the arcuate chamber containing the fluid. Fluid within the chamber is propelled by friction with the impeller vanes and, with suitable restraints in the chamber, the fluid head is increased in the direction of fluid flow. H. W. Iversen, "Performance of the Periphery Pump," Transactions of the ASME, January 1955, pages 19-28, provides a theoretical background discussion of periphery pumps of this character.
Design constraints and specifications for fuel pumps in aircraft turbine engine fuel delivery systems are such that periphery pumps of the subject character conventionally cannot be employed. For example, fuel pressure and flow requirements during low-speed starting typically are such that positive displacement pumps, such as vane-type pumps, must be employed. System designs specifications typically require fuel pumps to operate at a specified flow rate with a vapor/liquid inlet ratio of 0.45, and with a net positive suction pressure or NPSP, which is the pressure at the pump inlet above true vapor pressure of the fuel, of 5 psi. Newer system specifications, however, require the 0.45 vapor/liquid inlet ratio capability over a wider engine flow range, and may even require a 1.0 vapor/liquid ratio with intermittent all-liquid or all-vapor operation. Furthermore, the NPSP requirements have been increased to 5 psi over the entire engine flow range, and in some cases even 3 psi over the engine flow range.
It is therefore a general object of the present invention to provide a rotary hydraulic periphery pump that is capable of satisfying flow requirements in aircraft turbine engine fuel delivery systems over an extended engine operating range, and that is adapted to operate at a vapor/liquid inlet ratio up to 1.0 without cavitation and at 3 psi NPSP over an extended engine fuel flow range. A further object of the present invention is to provide a fuel pump of the describe character that is economical and efficient in construction in terms of the stringent weight and volume requirements in aircraft applications, and that provides reliable service over an extended operating lifetime.